There are many injectors on the market where the aim is to have high degrees of functionality and automatic features, such as in connection with penetration, injection, setting of dose, priming and covering of the needle after use. At the same time there is a demand on robustness, repeatability and reliability regarding the function, which sometimes might be difficult to meet when dealing with complex multi functions involving many interacting components. When there further are demands on low production costs, especially for devices that are to be used only once, the picture becomes even more complex.
There are in the patent literature numerous solutions to injection devices, the bulk of which never enter the market due to that they do not meet the demands in one way or the other. There is therefore a continuous search for solutions that provide the desired functions that at the same time fulfill the functional and/or economical demands.
Many devices having multi-functions that work in sequence, such as for example penetration, followed by injection, followed by withdrawal, have a subsequent sequence triggered at the end of a previous sequence, for example when the needle has reached full penetration depth, the injection sequence is triggered.
The drawback with this solution, especially when several components are interacting with each other in order to perform the sequences and the triggering of them, is that the tolerance and functional demands are increased in order to ensure that the subsequent sequence is really triggered at the end of the previous sequence. Should there be a tolerance error or a mismatch between two interacting components for triggering a subsequent sequence, the previous sequence will come to an end without triggering the next sequence. This may lead to a fatal situation if for example the injection of medicament is not performed.
In view of cost efficiency, high tolerance demands in order to achieve the desired chain of functions, are not advantageous, in particular when mass-producing injection devices.